The present invention relates to alkene-platinum-silyl complexes described by formula (I) (COD)Pt(SiR13xe2x88x92n)2Yn, where each R1 is independently selected from organic groups, halo atoms, and siloxy groups, each Y is an independently selected divalent bridging group between the silicon atoms bonded to platinum, n is 0, 1, 2, or 3, and COD is 1,5-cyclooctadiene.
Platinum compounds and complexes are well known catalysts for organic reactions, such as hydrosilation (or hydrosilylation), generally in amounts 5 to 100 parts per million mol per mol non-aromatic, multiple bond. Many so-called homogeneous platinum hydrosilation catalysts including the well-known Speier""s Catalyst and Karstedt""s Catalyst, though widely used, suffer from one or more disadvantages, such as loss of active platinum via precipitation at higher temperatures, slow catalysis rates for bulky or deactivated alkenes and concurrent side reactions, such as isomerization of the olefin. It is therefore desirable to find platinum hydrosilation catalysts that overcome one or more of the above disadvantages suffered by many known general purpose catalysts, and are also readily prepared, relatively inexpensive, and can provide high rates of reaction. A further positive attribute in such catalysts would be the ability to reuse the initial charge of catalyst without loss of activity, since platinum is a rare and precious metal with very low natural abundance.
The inventors have now discovered novel alkene-platinum-silyl complexes which are highly active catalysts and meet the above desirable qualities of robustness, homogeneity, ready synthesizability and maintenance of activity for repeated use.
The present invention is a class of alkene-platinum-silyl complexes described by formula (I)
(COD)Pt(SiR13xe2x88x92n)2Yn,
where each R1 is independently selected from organic groups, halo atoms, and siloxy groups, each Y is an independently selected divalent bridging group between the silicon atoms bonded to platinum, n is 0, 1, 2, or 3, and COD is 1,5-cyclooctadiene. A method of making these complexes is also described.
The present invention is a class of alkene-platinum-silyl complexes described by formula (I)
(COD)Pt(SiR13xe2x88x92n)2Yn,
where each R1 is independently selected from organic groups, halo atoms, and siloxy groups, each Y is an independently selected divalent bridging group between the silicon atoms bonded to platinum, n is 0, 1, 2, or 3, and COD is 1,5-cyclooctadiene.
In formula (I), each R1 is independently selected from organic groups, halogen atoms, and siloxy groups. The term xe2x80x9corganic groupsxe2x80x9d as used herein means groups having carbon chains or rings and the substituents bonded to those carbon chains or rings may include hydrogen atoms, halo atoms and oxygen, where the oxygen may also be connecting two carbon chains or bonded directly to a silicon atom. Preferred organic groups include alkyl groups comprising 1 to 25 carbon atoms, aryl groups comprising 6 to 25 carbon atoms, and oxygen-containing organic groups.
The alkyl groups comprising 1 to 25 carbon atoms of R1 may be linear, branched or cyclic. The alkyl groups may also be unsubstituted or substituted with halo atoms or oxygen groups. Examples of unsubstituted alkyl groups of R1 include methyl, ethyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, dodecyl, octadecyl, cyclopentyl, cyclohexyl, cyclohexylmethyl, 2-cyclohexylethyl, and norbornyl. Examples of substituted alkyl groups of R1 include chloromethyl, 3-chloropropyl, 3,3,3-trichloropropyl, 3,3,3-trifluoropropyl, fluorocyclohexyl, and methoxycyclohexyl. Preferred alkyl groups are methyl, ethyl, and 3,3,3-trifluoropropyl, with methyl and 3,3,3-trifluoropropyl being most preferred.
The aryl groups comprising 6 to 25 carbon atoms of R1 may be unsubstituted or substituted with halo atoms or oxygen groups. Examples of unsubstituted aryl groups of R1 include phenyl, tolyl, xylyl, biphenyl, benzyl, and naphthyl. Examples of substituted aryl groups of R1 include chlorophenyl, methoxyphenyl, and pentafluorophenyl. Preferred aryl groups are phenyl, tolyl, and chlorophenyl.
The oxygen-containing organic groups of R1 are groups having an oxygen radical bonded either directly to a silicon atom, connecting two carbon chains or as a substituent of a carbon chain. Preferred oxygen-containing organic groups include alkoxy groups and acyloxy groups.
The alkoxy groups have a formula described by xe2x80x94OR2, where R2 is an alkyl group comprising 1 to 25 carbon atoms. The alkyl group of R2 may be substituted or unsubstituted. Examples of R2 are as described above for the alkyl groups of R1. Specific examples of alkoxy groups useful in the invention include methoxy, ethoxy, 2-chloroethoxy, tertiarybutoxy, 2,2,2-trifluoroethoxy, pentoxy, cyclohexoxy, methoxyethoxy, bromocyclohexoxy, and methylcyclohexoxy. Preferably, R2 is an alkyl group comprising 1 to 6 carbon atoms.
The acyloxy groups have a formula described by xe2x80x94O(Cxe2x95x90O)xe2x80x94R3, where R3 is independently selected from alkyl groups comprising 1 to 25 carbon atoms and aryl groups comprising 6 to 25 carbon atoms. The alkyl groups and aryl groups of R3 can be substituted or unsubstituted. Examples of the alkyl groups comprising 1 to 25 carbon atoms and aryl groups comprising 6 to 25 carbon atoms of R3 are as described above for R1. Specific examples of acyloxy groups useful in the invention include acetoxy, propionyloxy, benzoyloxy, chloroacetoxy, dichloroacetoxy, trichloroacetoxy, and trifluoroacetoxy. Preferably, R3 is an alkyl group comprising 1 to 6 carbon atoms, most preferably R3 is a methyl group.
In formula (I), each R1 may also comprise halo atoms. Examples of these halo atoms include chloro, bromo, fluoro, and iodo atoms. Preferred halo atoms are chloro, bromo and fluoro, with chloro and bromo being most preferred.
Each R1 may also comprise siloxy groups. It is preferred that the siloxy groups have the formula xe2x80x94(OSiR42)nxe2x80x94X, where each R4 and X are independently selected from alkyl groups comprising 1 to 25 carbon atoms, aryl groups comprising 6 to 25 carbon atoms, halo atoms, and oxygen-containing organic groups and n is 1 to 6. Examples of the alkyl groups and aryl groups of R4 and X are as described above for R1. Examples of oxygen-containing organic groups are also as described above for R1. Preferred siloxy groups include xe2x80x94OSiMe3, xe2x80x94OSiMe2Ph, xe2x80x94OSiMe2CH2CH2CF3, and xe2x80x94OSiMe2OSiMe3, where Me means methyl and Ph means phenyl.
It is most preferred that each R1 is independently selected from methyl, phenyl, 3,3,3-trifluoropropyl, and chloro.
In formula (I), each Y group is an independently selected divalent bridging group between the silicon atoms bonded to platinum. This divalent bridging group may be comprised of xe2x80x94(OSiR12)mxe2x80x94Oxe2x80x94 units, where R1 is as described above and m is from 0 to 3, or divalent hydrocarbon groups comprising 1 to 5 carbon atoms. For example, the bridged siloxy structure may be based on linear siloxanes, cyclic siloxanes or silsesquioxanes, and the bridging hydrocarbon structure may be an alkylene such as xe2x80x94CH2CH2xe2x80x94 or an arylene such as ortho-phenylene.
Subscript n describes how many R1 groups and Y groups are bonded to each silicon atom bonded to platinum. Subscript n is an integer from 0 to 3. Preferably n is 0 or 1.
The other important ingredient of the present invention is COD which is 1,5-cyclooctadiene. The COD is bound to platinum in an eta-4 bonding mode.
Another embodiment of the present invention relates to methods of contacting COD, platinum, and SiH-containing silanes or siloxanes in sufficient amounts to make the alkene-platinum-silyl complexes described by formula (I) (COD)Pt(SiR13xe2x88x92n)2Yn, where R1, Y, n, and COD are as described above. These methods include premixing the COD and SiH-containing silane or siloxane prior to the addition of the platinum and premixing the COD and platinum prior to the addition of the SiH-containing silane or siloxane. In each case, the COD and SiH-containing silane or siloxane are added in amounts sufficient to form the alkene-platinum-silyl complex described by formula (I).
The platinum used in the above method can be a metal salt or complex, usually including anionic ligands such as halides or acetates. Examples of the platinum useful in this method include platinum diacetate, bis(acetylacetonate) platinum, PtCl2, H2PtCl6, PtCl4 and CODPtCl2. Preferred platinum complexes are PtCl2 and CODPtCl2 because of their ease of use. The platinum may be a single species or a mixture of two or more species.
The SiH group can be bonded to a silane molecule or siloxane molecule. There may be one or more SiH groups per silane or siloxane molecule. Examples of SiH-containing silanes useful in the above method include HSiMeCl2, HSiCl3, ClMe2SiH, PhMe2SiH, 1,2-bis-dimethylsilylethane, and 1,2-bis-dimethylsilylbenzene where Me means methyl and Ph means phenyl. Examples of SiH-containing siloxanes useful in the above method include 1,1,3,3,5,5-hexamethyltrisiloxane, pentamethyidisiloxane, (HSiO3/2)8, 1,1,2,2-tetramethyidisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane. The SiH-containing silane or siloxane may be a single species or a mixture of two or more species
The amounts of COD, platinum and SiH groups required to make the alkene-platinum-silyl complexes of the present invention will differ depending on what type of platinum is used. Generally, for every anionic ligand (for example halide, acetate etc.) to be removed from platinum there should be at least 1 SiH group added. Two additional SiH groups for each atom of platinum are also needed to meet the compositional requirement of the catalyst structure. The upper limit of SiH groups which can be used will depend on the reaction conditions; however if a several-fold excess is used the alkene-platinum-silyl complex will not form or may be rapidly destroyed. Preferably, the minimum number of SiH groups needed is the number of anionic ligands on platinum to be removed as silane (as opposed to a non-reactive salt) plus 2. Therefore, if using PtCl2or CODPtCl2 at least 4 SiH groups are required for each PtCl2or CODPtCl2 molecule, preferably 4 SiH groups on the same basis. If the alkene-platinum-silyl complexes is to be made in situ during a hydrosilation reaction, then it is not necessary to separately add SiH groups for every anionic ligand on platinum because the catalyst forms in-situ from the SiH groups of the silane added and then starts the hydrosilation catalysis of the alkene with the further SiH added.
The amount of COD added to the reaction mixture is critical in that there always must be close to at least 3 moles COD added for each mole of platinum. The total amount of COD required is determined partly by the amount of SiH used, since for every SiH used to remove an anionic ligand, the H component must be removed via hydrogenation. Preferably, there should be from 3 to 20 moles of COD added for each mole of platinum, the upper limit of COD is only determined by any detrimental effect of the excess COD on catalyst activity in hydrosilation. Some of the COD may be added to the mixture already bonded to platinum, for example, if added as (COD)PtCl2, or it could all be added as a separate component.
The order of addition of the ingredients COD, platinum and SiH-containing silanes or siloxanes is important to the formation of the alkene-platinum-silyl complexes. Generally, when the SiH-containing silane or siloxane contacts platinum, the COD must also be present. However, it is not critical whether the COD and SiH-containing silane or siloxane are premixed prior to addition to the platinum or whether the COD and platinum are premixed prior to the addition of the SiH-containing silane or siloxane. The preferred order of addition for preparing the alkene-platinum-silyl complexes of the present invention is the addition of the SiH-containing silane or siloxanes to a mixture of platinum and COD.
The contacting of the ingredients is by any method known in the art. Preferably, the contacting is by mixing with a mechanical stirrer or mixer. The contacting is preferably done with the reactants in a suitable solvent, although a neat reaction may be feasible. The solvent can be polar or non-polar, but polar solvents are preferred for faster reaction. Solvents which are known to complex with platinum, or that are discovered to complex with platinum should be avoided. Examples of suitable solvents include benzene, toluene, dichloromethane, chloroform, and 1,2-dichloroethane.
The temperature that the reaction is run at is not critical provided each of the reactants remains in the mixture. However, it should be understood that different SiH-containing silanes or siloxanes react under different conditions of temperature, pressure or solvent. Generally, the reaction can be run at temperatures from about 20xc2x0 C. to 100xc2x0 C. and temperatures from 32xc2x0 C. to 70xc2x0 C. are preferred. If necessary to ensure the reactants remain in the mixture at the temperature the reaction is being run, pressure can also be added.
A preferred alkene-platinum-silyl complex described by Formula (I) where n is 0 may be prepared as follows:
CODPtCl2+2(COD)+4MeCl2SiHxe2x86x92(COD)Pt(MeSiCl2)2+2(COE)+2MeSiCl3
where COD is as described above, Me is methyl, and COE is cyclooctene. Although not wanting to be tied to any theory, the inventors believe the two key reactions in the above process are removal of chloride from platinum as chlorosilane and removal of the H from SiH via hydrogenation of COD.
The alkene-platinum-silyl complexes of the present invention are useful as catalysts for hydrosilation reactions. The alkene-platinum-silyl complex can be added separately to the reaction mixture or formed in situ during the hydrosilation reaction.
Generally, hydrosilation products can be made by mixing ingredients comprising (A) at least one silane or siloxane having at least one non-aromatic, carbon-carbon multiple bond or at least one organic material having at least one non-aromatic, carbon-carbon multiple bond; (B) at least one silane or siloxane having at least one SiH group; and (C) an alkene-platinum-silyl complex described by formula (I) (COD)Pt(SiR13xe2x88x92n)2Yn, where R1, Y, n and COD are as described above.
There are many methods which can be utilized to form the alkene-platinum-silyl complex in situ during a hydrosilation reaction. For example, one could mix COD, platinum, and at least one silane or siloxane having at least one non-aromatic, carbon-carbon multiple bond or at least one organic material having at least one non-aromatic, carbon-carbon multiple bond, and then add to the premix at least one silane or siloxane having at least one SiH group.
Another in situ method includes mixing COD, at least one silane or siloxane having at least one SiH group, and at least one silane or siloxane having at least one non-aromatic, carbon-carbon multiple bond or at least one organic material having at least one non-aromatic, carbon-carbon multiple bond, and then adding the platinum to the premix.
A further in situ method includes mixing platinum, at least one silane or siloxane having at least one SiH group, and at least one silane or siloxane having at least one non-aromatic, carbon-carbon multiple bond or at least one organic material having at least one non-aromatic, carbon-carbon multiple bond, and then adding COD to the premix.
With each of these methods the order of addition of each of the ingredients forming each premix is critical in that the silane or siloxane having at least one non-aromatic, carbon-carbon multiple bond or at least one organic material having at least one non-aromatic, carbon-carbon multiple bond must be present before or at the same time as the silane or siloxane having at least one SiH group is mixed with platinum. However, when the catalyst forms in situ during a hydrosilation reaction, it is not necessary to add SiH-containing groups separate from the SiH-containing silane or siloxane used for the hydrosilation.
The SiH-containing silanes and siloxanes, the silanes or siloxanes having at least one non-aromatic, carbon-carbon multiple bond, and the organic materials having non-aromatic, carbon-carbon multiple bonds useful in these hydrosilation reactions can include any of such materials known in the art.